*added CTerrain::getSlopeAngle[Face]() which returns the angle in
radians of the slope of the terrain. getSlopeAngleFace should be used
for entities because it takes into account which way the entity is
facing, which allows for negative angles.
*the max and min graphical rotation for the slope is under traits.pitch.
This is used so that you can have certain units such as infantry that
don't rotate very far go down steep slopes but not rotate too much.
*JS documentation in docs/JSReg.rtf -- I put in most of the relevant
global functions; still needs entity functions.
This was SVN commit r3794.
